The present invention relates to methods of producing X-ray grids.
It is known to produce X-ray grids by mechanically glueing alternating X-ray transmitting and X-ray non transmitting layers. However, the mechanical process of their manufacture is difficult. Also, an X-ray grid is known which is composed of a monolithic panel with openings and a coating which is composed of an X-ray absorbing material. The monolithic panel is composed of a light sensitive glass and is exposed by a light beam passing through a mask which corresponds to a pattern of the X-ray grid. This method has certain limitations with respect to thickness of the panel and a relatively low accuracy of the finished grid due to distortions of the light beam at the edges of the mask and openings.
Finally, in accordance with another method an X-ray grid is produced from a light-sensitive glass which is exposed through a thin shaping device or mask so that various areas of the panel are exposed with different intensities, and then the image produced by the exposure is developed by heating, and the panel is etched in an aqueous solution of hydrofluoric acid, so that a grate is produced by forming of openings which are made in the exposed areas and separated by partitions in non-exposed areas. The thusly produced panels are glued together as layers so that the axes of the openings coincide with each other, and a grid of the desired thickness is produced. The glass can be an X-ray absorbing glass, or its inner walls of the openings can be covered with an X-ray absorbing coating.
In this method in order to produce a finished X-ray grid, several thin dispersing grates are assembled to form a grid, and each layer must have openings aligned with the openings of the neighboring layers. This method requires assembling of the layers so that a great numbers of openings can be aligned with each other and directed to a common focal point of the grid. For example, with the optimal number of strips 30 per cm, the number of openings in the cellular grid per 1 cm.sup.2 is 900; and with the efficient area of the grid 340.times.420 mm the number of openings in each layer of the grid is 1 398 600. It is evident that it is difficult to manufacture such panels having such great number of openings with high accuracy with exact coincidence of the openings and the partitions, or actually practically impossible. Utilization of electromagnetic radiation with a relatively great wavelength which is commensurate with the wavelength of the ultraviolet region of the spectrum leads to distortions of the formed image through the thickness of the exposed panel due to refraction, reflection and dispersion in the exposed glass of the rays which form the image, and the absolute value of the distortion increases with the increase of the thickness of the exposed panel. When the flat shaping device is utilized, substantial distortion of the formed images of elements of an X-ray grid does not permit obtaining of a non-distorted three-dimensional image of the grid in the panels of the substantial thickness, for example when it is necessary to provide the grid ratio of 6, 8, 12, etc. This is why it was necessary to make a composite grid. This method also cannot be used for making parallel X-ray grids, since it involves the use of only a pointed radiation source.